US Vice President Mike Pence, while saying he couldn't comment on classified information, restated his country's desire to identify those who had carried out the killing.

He said: "The murder of Jamal Khashoggi was an atrocity. It was also an affront to a free and independent press and the United States is determined to hold all of those accountable who are responsible for that murder."

On Saturday, the Trump administration denied it had reached a final determination over Mr Khashoggi's death.

In a statement, the state department said "recent reports indicating that the US government has made a final conclusion are inaccurate".

The Post claimed the CIA had information that Prince Mohammed's brother - the Saudi ambassador to the United States - told the late journalist by phone it would be safe to go to the consulate in Istanbul and get the papers he needed.

The ambassador, Prince Khalid bin Salman, swiftly denied that he had spoken with Mr Khashoggi on the phone or that he suggested he go to Turkey "for any reason".

"The last contact I had with Mr Khashoggi was via text on Oct 26 2017. I never talked to him by phone and certainly never suggested he go to Turkey for any reason," the prince wrote on Twitter. "I ask the US government to release any information regarding this claim."

He went on to post a full response to the Washington Post story, which said the claims in the CIA's "purported assessment are false. We have and continue to hear various theories without seeing the primary basis for these speculations".

The kingdom's public prosecutor Saud al Mojeb said in a statement that 21 people were now in custody over the killing, with 11 people indicted and facing trial.

The highest-level official accused of being behind the murder is former deputy intelligence chief Ahmad al Assiri, according to the prosecutor's spokesman Shaalan al Shaalan.

He said the Washington Post columnist's alleged killers had set in motion plans for the murder on 29 September, three days before he died inside the kingdom's consulate in Istanbul.

The public prosecutor's office appeared to distance the alleged killers and their operation from the Saudi Crown Prince and accused two senior officials of giving the orders.

Mr al Shaalan denied Prince Mohammed had any knowledge of the killing.

Earlier on Friday, Turkish President Recep Tayyip Erdogan and US President Donald Trump spoke on the phone and agreed on the need to prevent any cover-up of the killing, according to a source close to the Turkish leader.

Turkish media also claimed authorities had further evidence to discredit Riyadh's version of events, including a second audio tape.

Image:Hundreds of people turned out to say prayers to the slain journalist